Analysis Head of the Lock The St. Lawrence Seaway Authority has not specifically defined the term "head of the lock" in its Seaway Handbook, with the result that masters/pilots may adapt its meaning slightly differently to suit their own judgment or understanding. Although it is possible for large vessels (most Great Lakes bulk carriers are over 200m) to have their bow near the tip of the bullnose or even slightly past the pointL/A2 (Limit of Approach2) and yet have their stern remain well inside the lock chamber, this was not the case with the 134m composite unit. Although the unit's bow may have slightly exceededL/A2, its stern was 10m outside the lock gates. The instruction to proceed to the head of the lock- and the subsequent comment that the vessel had been instructed to remain within the lock- were contradictory. Moreover, the master of the PetiteForte had been traversing the Welland Canal as a master on many voyages in the previous seven years and had covered this route many times. He was familiar with the term and in this occurrence proceeded to go to a position he had taken on previous occasions when given the same instruction. However, he failed to question the second, contradictory, comment from the traffic controller that the vessel had been instructed to remain in the lock. Without a specific definition for the head of the lock, pilots/masters may position their vessels at risk. Lock Operations Vessel Monitoring After the line-handlers at Lock 4 let go of the composite unit, they tracked the vessel's stern as it moved downbound, beyond the lock gates and CNRail Bridge No.6. The bridge remained open and the line handlers began to focus their attention on the incoming vessel, Algomarine, which was approaching the lock's west chamber. Because the stern of the tug-barge unit was now located approximately 10m outside the lock gates and beyond the open bridge, lock personnel, having advised traffic control that the tug/barge unit had cleared Lock4, were not required to communicate further with the tug. In preparing to receive the next vessel into the lock, lock personnel lowered the arrester cable behind the tug-barge unit. However, the PetiteForte master was not informed of this event, nor was there an official requirement for Seaway Welland to do so. With their attention now shifted to the west chamber and the approaching Algomarine, lock personnel did not monitor the movement of the tug and barge when it began to move astern, towards the arrester cable. Discontinued spotting of the vessel and lowering the arrester cable without informing the master precluded him from positioning his vessel safely. Communications At 0602, the initial controller had instructed the PetiteForte to proceed to the head of the lock and hold position. At 0612, the new controller, who had just completed an information exchange with the previous controller prior to beginning his shift, issued a new comment- that the vessel had been instructed to hold position inside the east chamber until the Algomarine entered the west chamber, along with a reminder to do so in the future. This new comment contradicted the original controller's instruction to proceed to the head of the lock. The first traffic controller's instruction set in motion a number of events, namely the composite unit proceeding from inside the lock chamber to the head of the lock, Lock 4 personnel shifting their attention towards the Algomarine, and the lowering of the arrester cable astern of the PetiteForte. Masters/pilots on vessels entering or leaving locks require clear and unambiguous instructions as to where they may safely position their vessels. In this instance, the comment from the new ship traffic controller to the tug's master contradicted the previous instruction. The master, however, did not seek to clarify the apparent contradictory statements of the two controllers and the vessel continued to drift astern without being apprised of the situation. Crewing Requirements/Lookout The St. Lawrence Seaway Corporation permits this vessel to have only one qualified person in the upper wheelhouse, provided a second qualified person is stationed in the lower wheelhouse. However, the visibility astern from that lower wheelhouse was limited and the lowered arrester cable difficult to see, particularly at night. Consequently, the vessel was without the benefit of an efficient lookout in that location as intended by the Seaway Corporation's dispensation. Arrester Cable Visibility Photo5, taken in daylight, shows the arrester cable as difficult to see against the background of Lock4. In darkness, when the area was lit by shore-side floodlights, the difficulty increased particularly since the cable was cast in partial shadow. The shore-side lighting and restricted view from the lower wheelhouse made the arrester cable difficult to detect. Discontinued spotting of the vessel and lowering the arrester cable without informing the master precluded him from positioning his vessel safely. The master allowed the vessel to drift astern and contact the arrester cable because he was unaware that it had been lowered. The shore-side lighting and restricted view from the lower wheelhouse made the arrester cable difficult to detect. The final instructions received from Seaway Control suggested that movement astern was not inappropriate.Findings as to Causes and Contributing Factors Discontinued spotting of the vessel and lowering the arrester cable without informing the master precluded him from positioning his vessel safely. The master allowed the vessel to drift astern and contact the arrester cable because he was unaware that it had been lowered. The shore-side lighting and restricted view from the lower wheelhouse made the arrester cable difficult to detect. The final instructions received from Seaway Control suggested that movement astern was not inappropriate. Without a specific definition for the term "head of the lock", pilots/masters may position their vessels at risk.Finding as to Risk Without a specific definition for the term "head of the lock", pilots/masters may position their vessels at risk. Safety Action Action Taken St. Lawrence Seaway Management Corporation Following this occurrence, the St. Lawrence Seaway Management Corporation instructed lock operators that vessels are to be informed when the arrester cable has been lowered or when the lock preparation cycle has begun. Additionally, the St. Lawrence Seaway Management Corporation has since covered arrester cables with a fluorescent yellow wrap to make them more visible for spotting purposes. A new procedure has been adopted that addresses lock responsibility regarding monitoring vessels which have been dispatched to "hold at the head of the lock."